Dibenzoylmethane derivatives are compounds that absorb the full spectrum of UVA radiation. The absorption of UVA radiation (at 320-400 nm) by a dibenzoylmethane derivative causes the excitation of an electron in the dibenzoylmethane derivative molecule from an initially occupied, lower energy orbital to a higher energy, previously unoccupied orbital. The energy of the absorbed photon is used to energize an electron and cause it to “jump” to a higher energy orbital. See Turro, Modern Molecular Photochemistry, 1991. Two excited electronic states derive from the electronic orbital configuration produced by UV light absorption. In one state, the electron spins are paired (antiparallel) and in the other state the electron spins are unpaired (parallel). The state with paired spins has no resultant spin magnetic moment, but the state with unpaired spins possesses a net spin magnetic moment. A state with paired spins remains a single state in the presence of a magnetic field, and is termed a singlet state. A state with unpaired spins interacts with a magnetic field and splits into three quantized states, and is termed a triplet state.
In the electronically excited state, the UV absorbing molecule, e.g., dibenzoylmethane derivative, is prone to degrade via a number of known pathways and, therefore, can absorb little or no additional UV light. To photostabilize an electronically excited, chromophore-containing, UV absorbing organic molecule in order to provide sufficient UV protection, it must be returned to the ground state before it undergoes a photochemical reaction destructive to its UV absorbing capability.
There are known photostabilizing sunscreen additives, such as Octocrylene, methylbenzylidene camphor, and the esters or polyesters of naphthalene dicarboxylic acid of this assignee's U.S. Pat. Nos. 6,113,931; 6,284,916; 6,518,451; and 6,551,605, all hereby incorporated by reference, that are capable of quenching excited triplet state energy from dibenzoylmethane derivatives. Surprisingly, it has been found that cyano-containing fused tricyclic compounds return chromophore-containing organic molecules, particularly butyl methoxydibenzoylmethane (Avobenzone), octyl methoxycinnamate (Octinoxate), and octyl salicylate (Octisalate), from either an electronically excited singlet state or excited triplet state back to their ground state, thereby photostabilizing the UV-absorbing organic molecules.
Deflandre U.S. Pat. No. 5,576,354 generally discloses a cosmetic sunscreen composition containing at least 1% by weight of an α-cyano-β,β-diphenylacrylate that will photostabilize a dibenzoylmethane derivative, e.g., Parsol 1789 (Avobenzone), so long as the composition contains a fatty phase, e.g., glycerol stearates, isopropyl myristate or the like, and so long as the mole ratio of the α-cyano-β,β-diphenylacrylate to the dibenzoylmethane derivative is at least 0.8.
Octocrylene is known to quench (accept) the excited triplet state energy of an excited photoactive compound by dissipating the energy kinetically in the form of rapid isomerizations. This process is shown below:
wherein the α-cyano-β,β-diphenylacrylate compound (octocrylene shown above as structure A), accepts the triplet excited state energy from a photoactive compound and forms a diradical (shown above as structure A*) at the α and β positions of the acrylate, which converts the double bond into a single bond and allows for the free rotation of the phenyl groups. This rotation occurs rapidly and efficiently to dissipate any excited triplet state energy accepted by the α-cyano-β,β-diphenylacrylate compound from the photoactive compound.
While octocrylene is able to quench (accept) the triplet excited state energy from a photoactive compound, thereby photostabilizing, to some degree, dibenzoylmethane derivatives, as shown in examples 1, 4, 6 and 8 of Deflandre et al. U.S. Pat. No. 5,576,354, there exists a need in the photoactive composition art to find one or more compounds that quench (accept) the singlet excited state energy and preferably also the triplet excited state energy from photoactive compounds, which octocrylene does not.
Quite surprisingly, it has been found that the cyano-containing fused tricyclic compounds described herein will quench excited state energy of UV-absorbing organic molecules, such as dibenzoylmethane derivatives, particularly Avobenzone, returning the excited UV-absorbing organic molecules to their ground state for additional UV absorption.